This invention relates generally to optical fibers and, more particularly, to fiber amplifiers and lasers.
Rare-earth doped fiber lasers have many potential applications in telecommunications, sensors, spectroscopy, laser radar, and medicine. They are widely recognized as efficient configurations for generating light in a single transverse mode.
Rare-earth doped fiber lasers generate laser light from de-excitations of rare-earth atoms that dope the fiber""s core. The rare-earth atoms are excited by an external pump source. The power from the pump source determines the laser""s output power. Generally, rare-earth fiber lasers are low power devices, because low power pump sources provide the power for the fiber lasers. High power pump sources, such as multi-spatial mode laser diodes, are difficult to couple to the doped cores.
For example, locating a single spatial mode diode laser near one end of the fiber enables pumping the rare earth dopants of the fiber core. Since the doped core typically has a narrow cross section, a small single mode diode laser is efficient for introducing pump light into the doped core. But, single spatial mode diode lasers produce pump light powers in the range of a few hundred milli-watts. When pumped by such a source, a rare earth doped core produces low powers in the range of about a hundred milli-watts.
Some fiber lasers enclose the doped core by a larger diameter cladding. In such lasers, pump light enters into the cladding and then, subsequently excites the doped core. Since the cladding diameter is larger, the cladding can capture light from larger pump sources, such as multi-spatial mode laser diodes. Nevertheless, the high power pump sources may still produce undesirable heating in the amplifying fiber.
In a first aspect, the invention is an optical amplifier. The optical amplifier includes first and second optical fibers. The first optical fiber has a core, a first cladding surrounding the core and a second cladding surrounding the first cladding. The second optical fiber has an end optically coupled to a side portion of the first optical fiber. The end transmits light to the first cladding.
In a second aspect, the invention is an optical fiber amplifier. The amplifier includes an optical fiber and an optical waveguide. The optical fiber has a core, a first cladding surrounding the core, and a second cladding surrounding the first cladding. The first cladding has a cross section adapted to redirect light traveling therein into paths intersecting the core. The optical waveguide couples to a side portion of the optical fiber.
In a third aspect, the invention is a method of amplifying a light signal. The method includes transporting light down an optical waveguide using total internal reflection, transmitting a portion of the transported light across a side surface of a double clad fiber. The method uses internal reflections to redirect most of the transmitted light along paths intersecting a core of the double clad fiber. The light intersecting the core generates an inverted population of exciting atoms therein.
Various embodiments provide high power amplifiers by side-pumping a multi-clad fiber with an optically excitable core.
Various embodiments provide high power amplifiers in which pumping heat is delocalized over the amplifying fiber instead of localized at one end.
Various embodiments provide a high power fiber amplifier in which the fiber""s ends are freely accessible.
Various embodiments provide a fiber amplifier which directly side-couple pumping fibers or optical conduits to the amplifying fiber.